Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, milk, egg, garlic powder, onion powder, salt, black pepper, and Worcestershire sauce. Mix until well combined.
Form the mixture into 16 meatballs and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for 20 minutes or until browned and cooked through.
While the meatballs are baking, bring water to a boil in a medium saucepan and add the cubed potatoes. Cook until tender, about 15 minutes, then drain.
Return the potatoes to the saucepan, add milk, butter, salt, and pepper, and mash until smooth and creamy.
In a large skillet, heat olive oil over medium heat and add the chopped onion, sautéing until translucent.
Stir in the beef broth, soy sauce, and dried thyme, allowing the mixture to simmer for a few minutes.
Add the cornstarch mixture to the skillet, stirring constantly until the gravy thickens, and then remove from heat.
Once the meatballs are cooked, transfer them to the skillet and coat them with the gravy.
Serve the Salisbury meatballs over a generous portion of mashed potatoes.
Enjoy your delicious meal!